Fiber reinforced thermoplastic composites generally include reinforcing fibers contained in a polymer matrix made from a thermoplastic polymer. The presence of the fibers can greatly increase certain mechanical properties of the polymer. The thermoplastic polymer, on the other hand, is capable of being formed into any suitable shape. Thus, many shaped parts in different industries can be made from polymer composite materials.
In one embodiment, shaped or molded parts made from polymer composites can be prepared from pellets of coated, long fiber reinforced composite structures. U.S. Pat. No. 6,090,319, for instance, which is incorporated herein by reference, describes generally a production process wherein continuous fibers are coated in a die and then cut to the desired length to form the pellets. The pellets are made according to a pultrusion process and can include any suitable thermoplastic polymer, such as a polyolefin, a polyamide, or mixtures thereof. Composite pellets are also disclosed in U.S. Pat. No. 6,844,059, U.S. Pat. No. 6,794,032, and U.S. Pat. No. 6,482,515, which are all incorporated herein by reference.
Shaped parts or structures can be formed from the composite pellets using any suitable process. In one embodiment, for instance, the shaped parts can be made through an injection molding process. In an injection molding process, the polymer and fiber material is heated above the softening temperature of the polymer and the resulting fluid polymer material is introduced into a mold in a manner that causes the polymer material to assume the interior shape of the mold.
In one particular embodiment, the composite polymer material is formed into a microcellular plastic foam during the injection molding process. For example, a blowing agent may be mechanically or chemically introduced into the polymer melt during the process which causes the foam to form. The blowing agent may comprise, for instance, a supercritical fluid. For example, U.S. Pat. No. 6,884,377 and U.S. Patent Application Publication No. 2005/0042434, which are incorporated herein by reference, disclose injection molding processes for producing polymer foam articles.
As stated in the '434 application, although the introduction of reinforcing fibers into molded polymer foam articles is known, one problem that has been encountered in the injection molding of these articles is that the fibers can break during the process, which can compromise the properties of the resulting articles. Thus, the '434 application is directed to injection molding polymer composite articles that results in less breakage of the reinforcing fibers. Although the process disclosed in the '434 application has shown to create less breakage of the reinforcing fibers, the present disclosure is directed to further improvements in injection molding processes for producing fiber reinforced foam polymer articles.